An infrared imaging device known as an imaging device measures the surface temperature of an object by non-contact in a remote position by incident infrared rays, and is used for detection of the form of the object. The infrared imaging device is used for wide uses, such as a measuring device and a control device in a manufacturing line, a diagnostic device in medical treatment, and a night vision camera and a sensor device, for example.
An infrared imaging device provides an image of the incident infrared rays by use of reflecting mirrors and lenses, and acquires an image by changing the infrared rays into an electric pixel signal. An infrared sensor array includes a plurality of sensor elements arranged in the shape of a two-dimensional matrix, and a readout circuit that reads out pixel data from the sensor elements, for example. The sensor elements and the readout circuit are formed on separate substrates, respectively, and are connected to each other via a conductive bump.
A substrate of the sensor elements is formed of gallium arsenide (GaAs) or the like, for example. On the other hand, a substrate of the readout circuit is formed of silicon (Si) or the like. These substrates are different from each other in material and linear thermal expansion coefficients are different from each other. Therefore, when the substrates are joined by flip chip bonding and the bump formed of a solder is heated for example, there is a problem that stress is applied to each substrate.
Therefore, there is used a method for joining the substrates by forming the bump with flexible metal such as indium (In), pressurizing it under the environment of normal temperature, and pressing one substrate against another substrate.
With respect to the infrared imaging device, for example, Patent Document (see Japanese Laid-open Patent Publication No. 2009-164302) and non-Patent Document (see “Demonstration of Megapixel Dual-Band QWIP Focal Plane Array”, IEEE JOURNAL OF QUANTUM ELECTRONICS, (United States of America), 2010 February, VOL. 46, NO. 2, p. 285) describe a double-wavelength QWIP (Quantum Well Infrared Photodetector) which has a sensitivity to the infrared rays with two wavelength ranges. The double-wavelength QWIP is provided with two Multi Quantum Well (MQW) layers which absorb the infrared rays with two wavelength ranges, respectively.